This invention relates generally to fluid filters and more particularly to filters for automotive fluids such as transmission fluids and to such filters with automatic clogged filter element bypass functionality. The invention also relates to indicator flags for indicting a clogged or failure condition in filters, conduits, and the like.
Automatic transmissions in modern vehicles are at least partially filled with automatic transmission fluid, which lubricates and cools the transmission and provides hydrostatic coupling between the engine and the driven wheels. In most cases, the automatic transmission fluid is circulated through a fluid flow conduit from the transmission, to a radiator, and back to the transmission to cool the fluid and prevent the transmission from overheating. Over time, small particles or flecks of ferrous metal tend to become suspended in the transmission fluid as a result of the normal wear and tear on internal working components of the transmission. Non-ferrous particles such as particles of aluminum, plastic, or dirt also can become suspended in the transmission fluid. These ferrous and non-ferrous particles become entrained in the transmission fluid as it circulates and, if not removed, can cause serious damage to the transmission as a result of their abrasive action on moving internal components thereof.
In order to remove particulates from automatic transmission fluid, transmissions are provided with filters. As the transmission fluid is circulated, it passes through these filters, which presumably trap and remove the particles from the fluid. One example of an automatic transmission fluid filter for removing ferrous and non ferrous particles from the fluid is disclosed in U.S. Pat. No. 4,689,144 of Holmes. The Holmes filter is an in-line filter unit that includes a cylindrical casing within which a cylindrical filter element is disposed. The casing has an inlet end provided with an inlet port and an outlet end provided with an outlet port and is coupled in-line with a transmission fluid circulation conduit, the transmission fluid passing through the filter unit as it circulates. An annular or donut shaped magnet is disposed at the inlet end of the casing and the transmission fluid flows through the central opening of the magnet and into the interior of the filter element through its porous outside wall before passing out of the housing through a spigot disposed in the filter element. In theory, ferrous particles entrained within the fluid are attracted to the magnet as the fluid flows through and around the magnet and non-ferrous particles are trapped by the filter medium of the filter element. In this way, the transmission fluid is continuously filtered to remove both ferrous and non-ferrous particles as the fluid is circulated during operation of the transmission.
Occasionally, the filter elements of in-line filters such as the filter unit disclosed in Holmes become clogged with trapped particles and fluid flow through the filter unit can become constricted. In order to prevent this situation from interrupting the circulation of transmission fluid, which can ruin or render inoperative the transmission, transmission fluid filters are provided with bypass functions. In Holmes, for instance, a pressure relief valve is mounted in the end of the filter element adjacent the inlet end of the casing. If the fluid pressure increases due to a clogged filter element, the pressure relief valve opens to allow transmission fluid to flow directly into the filter casing and out through the spigot and outlet port without passing through the clogged filter medium of the element. While this clearly eliminates the filtering function of the filter element, it nevertheless allows transmission fluid to continue to circulate and the transmission to continue to operate. The fluid still passes through the annular magnet, however, so that ferrous particles, in theory, are still removed from the fluid. In other in-line fluid filters, such as that disclosed in U.S. Pat. No. 4,166,792 of Offer et al., increased fluid pressure as a result of a clogged filter element causes the filter element itself to move within the casing against a biasing spring to allow the fluid to flow directly around and bypass the clogged element.
In prior art transmission fluid filters, the magnets that remove ferrous particles from the fluid are fixed within the filter casings. As a result, the surface area of the magnet to which the fluid is exposed when the filter element becomes clogged and the unit is in bypass mode is relatively small. Furthermore, in filter units where the filter element itself moves away from the magnet when clogged to provide fluid bypass, the force of the fluid against the now exposed open end of the filter element can cause turbulence. This turbulence, in turn, can stir up and disturb trapped particles within the clogged filter element, which become re-entrained in the fluid flow and can cause damage to a transmission. Finally, it has been observed that the bypass function of in-line filters is only gradually activated as the filter elements of the filters slowly become clogged. This can contribute to the stirring up of trapped particles in the clogged filter as a result of fluid turbulence. Thus, prior art automatic transmission fluid filters have not proven to be complete solutions to the problems of filtering particles from circulating transmission fluid while at the same time insuring that fluid circulation is not affected when the filter elements of the filters become clogged.
A need exists, therefore, for an in-line automatic transmission fluid filter that traps ferrous and non-ferrous particles entrained within the fluid as the fluid circulates and that provides effective bypass of the filter element when the element becomes clogged. More specifically, a clogged condition of the filter element should result in an immediate complete bypass condition rather than a gradual transition to the bypass condition in order to eliminate the stirring up of particles within the clogged filter element by fluid turbulence. When in a bypass condition, fluid flowing through the filter should be exposed to a clean and relative large magnet surface area to insure the continued removal of ferrous particles from the fluid even when the filter element is bypassed. Finally, fluid turbulence at the mouth of and within the clogged fluid filter during a bypass condition should be minimized, again to minimize or eliminate the stirring up and re-entraining of particles in the fluid. A further need exists for a reliable and simple means of indicating visually when the filter is clogged so that it can be replaced with a fresh filter. Indeed, a need exists in general for reliable and simple indicator flag systems for indicating visually a failure condition in various types of systems including a restricted flow through a fluid flow conduit or spent battery acid in an automotive battery. It is to the provision of such an in-line filter unit and to such indicator flags that the present invention is primarily directed.
Briefly described, the present invention, in a preferred embodiment thereof, comprises a filter unit for removing ferrous and non-ferrous particles from a flow of fluid through a fluid flow conduit. The filter unit includes a generally cylindrical casing having a diameter, an inlet end formed with a fluid inlet port, and an outlet end formed with a fluid outlet port. The inlet and outlet ports, which may be of the quick-disconnect type, are adapted for coupling the casing in-line with the fluid flow conduit so that fluid flows through the casing from its inlet end to its outlet end.
A generally cylindrical filter element has a diameter smaller than the diameter of the casing and is disposed within the filter casing. The filter element has a first end formed with an opening and being located adjacent the inlet end of the casing and a second end located adjacent the outlet end of the casing. A generally annular magnet having an outside diameter smaller than the diameter of the casing is mounted to the first end of the filter element. The magnet is formed with an opening substantially aligned with the opening formed in the first end of the filter element.
The filter element is movable within the casing between an operational position wherein the magnet is seated against the inlet end of the casing for fluid flow through the opening in the magnet and into the filter element, and a bypass position wherein the magnet is displaced from the inlet end of the casing for fluid flow around the magnet and around the filter element. A spring may be disposed in the casing, preferably between the second end of the filter element and the outlet end of the casing, for yieldably biasing the filter element to its operational position during normal operation of the filter unit. Alternatively, the spring may be eliminated and the inlet end of the filter casing formed of a ferrous material. In such an embodiment, the filter element is held in its seated position against the inlet end of the casing by magnetic attraction between the magnet on the end of the filter element and the ferrous inlet end of the casing.
During normal operation, fluid passes through the opening in the magnet, into the filter element through its open end, through the filter media that forms the sides of the filter element, and out of the filter unit through the outlet port. The magnet attracts and removes from the fluid any small ferrous particles that may be entrained in the fluid and the filter element filters and removes non-ferrous particles from the fluid.
When the filter element becomes clogged, the resulting fluid pressure moves the filter element to its bypass position, wherein the magnet is displaced from the inlet end of the casing. In this bypass condition, fluid is allowed to bypass the clogged filter element while continuing to pass over and around the magnet. Thus, the magnet continues to attract and trap ferrous particles within the fluid. In addition, the surface of the magnet presented to the fluid is clean and of substantially greater area than the interior surface surrounding the central opening of the magnet. Thus, removal of ferrous particles in the bypass mode is enhanced and continues even though non-ferrous particles are not being filtered by the filter element. Further, the opening of the magnet helps prevent turbulence in the fluid from stirring up and dislodging particles previously trapped within the filter element. Periodic inspection will reveal the clogged condition of the filter element and the filter unit can be replaced with a fresh unit easily as a result of the quick disconnect inlet and outlet ports.
A horseshoe or other shaped ferrous indicator flag may be provided for indicating when the filter unit is operating normally and when it is clogged. More specifically, the indicator flag, which may be colored orange or another bright color, is position on the exterior of the casing in the region where the magnet of the filter element resides when the filter is operating normally. So long as the filter element is in its normal position within the casing, the magnet remains in this region and, since the indicator flag is ferrous, holds the indicator flag to the exterior of the casing by magnetic attraction. However, when the filter element becomes clogged and moves to its bypass position as discussed above, the magnet moves down with the filter and away from the region where the indicator flag is located. When this happens, the indicator flag simply falls away from the exterior of the casing. This, the absence of an indicator flag serves as a visual indication that the filter unit is clogged and requires replacement. The indicator flag also may be configured to cover a bright colored strip or bright words such as xe2x80x9creplace filter element.xe2x80x9d In such an embodiment, when the flag falls away from the exterior of the casing, it reveals the strip or words as a more vivid indicator that replacement of the filter unit is required. This magnetic indicator flag technology also may be applied to other systems to, for example, indicate when battery acid in a battery is spent and the battery requires replacement or to indicate when fluid flow through a conduit is below or above established limits. Finally, a hall effect or magnetic reed switch may be used in place of a ferrous indicator flag with the switch connected to activate an indicator light within the vehicle when a clogged or failure condition occurs.
Accordingly, a filter unit, particularly suited for filtering automatic transmission fluid, is now provided that successfully addresses the problems and shortcomings of the prior art. More specifically, in normal operation, the unit traps ferrous and non-ferrous particles and removes them from the fluid flow. When the filter becomes clogged, the unit reverts to a bypass condition, in which ferrous particles are still removed efficiently and in which turbulence that might otherwise dislodge trapped particles from the clogged filter and re-entrain them in the fluid is greatly reduced. The unit is easily replacable with a fresh unit because of its quick disconnect inlet and outlet ports. The ferrous indicator flag provides a simple and reliable visual indication of a clogged condition of the filter unit so that replacement can be made promptly. These and other features, objects, and advantages of the filter unit of this invention will become more apparent upon review of the detailed description set forth below when taken in conjunction with the accompanying drawing figures, which are briefly described as follows.